The present invention relates to a multifocal ophthalmic lens, having an aspherical surface which has a mean sphere and a cylinder at every point thereon.
Such lenses are well known; among multifocal lenses one can distinguish lenses known as progressive lenses adapted to vision at all distances, and lenses that are more specifically dedicated to near vision and intermediate vision.
Progressive multifocal ophthalmic lenses comprise a far vision region, a near vision region, an intermediate vision region, and a main meridian of progression passing through the three regions. French patent application 2,699,294, which is incorporated herein by reference, describes, in its preamble, the various elements of a progressive multifocal ophthalmic lens (main meridian of progression, far vision region, near vision region, etc.), as well as the work carried out by the applicant to improve wearer comfort of such lenses.
Applicant has also proposed, in order to better satisfy the visual needs of long sighted people and to improve comfort of progressive multifocal lenses, to adapt the shape of the main meridian of progression, as a function of the power addition value A (French patent application FR-A-2,683,642).
For such lenses, the power addition value A is defined as the variation in mean sphere between a reference point in the far vision region and a reference point in the near vision region.
Such progressive lenses are generally prescribed as a function of the wearer's ametropia and the power needed for near vision.
Lenses also exist which are more specifically dedicated to near vision; such lenses do not have a a far vision region with a defined reference point like conventional progressive lenses have. Such lenses are prescribed depending on the near vision power the wearer needs, independently of the far vision power. Such a lens is disclosed in an article in the "Opticien Lunetier" dated April 1988, and is sold commercially by the applicant under the Essilor Delta trademark; this lens is also as simple to use and easy to wear as a progressive lens, and it is attractive to long-sighted people not fitted with progressive lenses. This lens is also described in French patent application FR-A-2,588,973. It has a central portion which is equivalent to the single-focus lens that would normally have been employed for correcting long sightedness, in order to ensure satisfactory near vision. It additionally has a slight decrease in power in the upper portion, ensuring that the wearer also has sharp vision beyond the usual near vision field. Finally, the lens has a point at a power value equal to the nominal power for near vision, a higher power region at the lower portion of the lens, and a lower powered region in the top portion of the lens.
Existing multifocal lenses, whether they be progressive or dedicated to near vision can still be further improved as regards their foveal vision performance, in order to improve wearer comfort. Wearers of multifocal lenses do in fact sometimes feel uncomfortable with dynamic vision. Such lenses can also be improved by preserving a near vision region that is sufficiently high to ensure optimum wearer comfort; finally, it is important that wide visual fields be provided in close, intermediate and far vision.